Intention is: let the offense team makes a 5-second count mistake or an interception of a poorly made pass from the in-bounder.
The defender (5) whose assigned person is the in-bounder gets back to at least half-court or beyond as the "safety" against the long pass and lay-up.

The other defenders (1-4) immediately locate their man and deny the pass from the in-bounder by playing the passing lanes and staying between their man and the ball, face to face and hands-up.

The (1-4) defenders should not worry about the long pass over their heads, as the "safety" (5) is back to stop that.